Antimicrobial composition for protecting wood

ABSTRACT

A multifunctional broad spectrum antimicrobial composition is described. The composition can be incorporated into a wood preservative, or used as an additive to provide antimicrobial properties to water-based wood coatings. The composition is a concentrated water-miscible emulsion containing 3-iodo-2-propynyl N-butylcarbamate (IPBC), carbendazim (BCM) and propiconazole (PPCZ), and has antimicrobial activity against a wide variety of fungal organisms, including surface molds, blue stain fungi and wood rotting fungi. The composition can act as an in-can preservative and is useful for antimicrobial protection of wood and wood-based substrates.

RELATED CASES

This application claims the priority of the PCT application serialnumber PCT/CA2015/000356 filed May 20, 2015. Applicant herebyincorporates by reference the entire content of PCT application serialnumber PCT/CA2015/000356. This is a divisional application of U.S.patent application Ser. No. 15/312,549 filed on Nov. 18, 2016. Thedisclosure of U.S. patent application Ser. No. 15/312,549 is expresslyincorporated by reference in its entirety.

BACKGROUND

The present application is directed to an antimicrobial composition forprotecting wood. More specifically, the present application is directedto a multifunctional broad spectrum antimicrobial composition which canbe incorporated into a wood preservative, or can be used as anantimicrobial additive in water-based wood and wood composite coatings.

Wood surfaces, such as those on buildings and other structures which areexposed to the environment, are susceptible to attack by microbes suchas fungi or bacteria and other pests. For example, in areas such as theLower Mainland of British Columbia, mold growth on attic roofcomponents, especially on wood framing and sheathing, can occur becauseof roof leaks or water vapor condensation. When air-borne fungal sporesand/or tiny air-borne mycelia fragments land on wet or damp woodsurfaces, initial mold culture can become established and laterproliferate into large colonies. Attempts to prevent the significantcondensation problem in such areas by re-designing roofs have not so farsuccessfully addressed the issue.

Fungal attack of wood surfaces can compromise or destroy the structuralintegrity of the wood, as well as damage its appearance. As well, moldcolonies can release high levels of mycotoxins to prevent invasion bycompetitive organisms. As a result, apart from cosmetic problems, moldgrowth can cause adverse health effects in humans, and considerablyreduce the commercial value of structures.

Coatings and preservatives for such wood surfaces therefore ofteninclude antimicrobial compounds to protect the wood from damage causedby such microbes. A wide variety of antimicrobial compounds are known tobe used in such wood preservatives and coatings. However, in many cases,such antimicrobial compounds are less effective against some speciesthan others, and may need to be present at relatively high levels tohave broad spectrum effectiveness against an adequate range of microbes.Alternatively, combinations of individual antimicrobial products, eachof which individually has effectiveness against a specific species orgroups of species, may be necessary to achieve broad spectrumeffectiveness against the desired range of microbes.

For some applications of wood coatings, it is desirable that suchantimicrobial compounds be present at low levels or absent. Many suchantimicrobial compounds can be harmful to humans or animals. Thus, if itis likely that humans or animals will come into contact with a coatedwood surface, it is desirable to prevent or minimize exposure topotentially harmful levels of antimicrobial compounds caused by suchcontact. Furthermore, in some cases, wood surfaces may not be exposed toan environment where attack by microbes is a substantial risk, andtherefore would not need a high level of antimicrobial protection. Insuch cases, there would be no need to risk exposing users to high levelsof antimicrobial compounds during application of a coating. Thus,manufacturers who wish to provide a choice of coatings to theircustomers must develop a number of different antimicrobial ornon-antimicrobial formulations at additional effort and cost.

Therefore, there is a need for an antimicrobial composition which can beconveniently stored and diluted as needed to provide a woodpreservative, or which can be added to wood preservative and woodcoating formulations so as to provide the formulations withantimicrobial properties as desired. In this way, coating manufacturerscan readily achieve alternative antimicrobial protection for existingcoatings without the need for costly or time-intensive research. In somecases, non-antimicrobial coatings, such as interior paints and stains,could be readily adapted for applications requiring antimicrobialproperties.

In addition, it is desirable to provide an antimicrobial compositionwhich has antimicrobial activity against a range of wood-attackingmicrobes, so as to reduce the need for treatment with multiple products,each containing individual antimicrobial agents.

SUMMARY

In one aspect, the present invention provides an antimicrobialcomposition, containing from about 10% to about 25% by weight of3-iodo-2-propynyl N-butyl carbamate (IPBC), about 12% to about 20% byweight of propiconazole (PPCZ), about 2% to about 8% by weight ofcarbendazim (BCM) and about 25% to about 70% by weight of a carrierfluid. The antimicrobial composition is in the form of an emulsion. Inat least one embodiment, the antimicrobial composition further containsabout 7% to about 15% by weight of an emulsifier. In at least oneembodiment, the antimicrobial composition further contains about 2% toabout 4% by weight of a co-emulsifier. In at least one embodiment, theantimicrobial composition further contains about 3% to about 14% byweight of an emulsion stabilizer. In at least one embodiment, theantimicrobial composition further contains about 0.3% to about 3% byweight of an antifoaming agent.

In another aspect, the present invention provides an antimicrobial woodpreservative comprising an antimicrobial composition as describedherein.

Another aspect of the present invention provides a method of preservingwood, comprising treating the wood with an antimicrobial woodpreservative as described herein.

A further aspect of the present invention provides the use of anantimicrobial composition as described herein in the preparation of anantimicrobial wood coating product comprising a water-based woodcoating.

In another aspect, the present invention provides a method of preparingan antimicrobial wood coating product comprising adding theantimicrobial composition as described herein to a water-based woodcoating to form a mixture; and agitating the mixture to form theantimicrobial wood coating product.

Yet another aspect of the present invention provides an antimicrobialwood coating product comprising a water-based wood coating and anantimicrobial composition as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application with color drawing(s)will be provided by the Office upon request and payment of the necessaryfee.

Further features of the present invention will become apparent from thefollowing written description and the accompanying figures, in which:

FIG. 1 is a diagram illustrating wood coated with a wood coating fromwhich antimicrobial agents have partially penetrated into the wood;

FIG. 2 is a photograph of lodgepole pine wood blocks treated with anantimicrobial wood preservative according to the present invention, andtested for mold growth in a controlled environment mold growth chamber;

FIG. 3 is a photograph of a typical attic in the Lower Mainland ofBritish Columbia which has been attacked by mold as a result ofcondensation due to high ambient relative humidity conditions (photocourtesy of RDH Building Engineering Ltd.);

FIG. 4 is a chart showing the degree of mold growth under simulatedattic conditions on Douglas fir plywood blocks treated with anantimicrobial wood preservative according to the present invention,treated with other products or untreated, or on untreated Ponderosa pinesapwood blocks;

FIG. 5 is a photograph showing zones of inhibition of growth of decayfungi around white pine sapwood blocks treated with an antimicrobialwood preservative according to the present invention or with a woodpreservative containing 3-iodo-2-propynyl N-butyl carbamate (IPBC) alone(photo: The Sansin Corporation);

FIG. 6 is a photograph showing the degree of mold growth on white pinesapwood blocks which are uncoated or coated with a clear wood coatingcontaining an antimicrobial composition according to the presentinvention or IPBC alone (the lid of the culture dish was removed for thephotograph; photo: The Sansin Corporation);

FIG. 7 is a photograph showing the degree of fungal growth on untreatedred pine sapwood cubes and red pine sapwood cubes treated with anantimicrobial wood preservative according to the present invention andexposed to brown rot fungus (photo courtesy of the Earth Science Center,Faculty of Forestry, University of Toronto);

FIG. 8A is a graph showing the average retention gradient of totalactive ingredients along the radial direction (end to end) of red pinesapwood cubes treated with an antimicrobial wood preservative accordingto the present invention before and after leaching (data courtesy of theEarth Science Center, Faculty of Forestry, University of Toronto);

FIG. 8B is a graph showing the average retention gradient of totalactive ingredients along the longitudinal direction (end to end) of redpine sapwood cubes treated with an antimicrobial wood preservativeaccording to the present invention before and after leaching (datacourtesy of the Earth Science Center, Faculty of Forestry, University ofToronto);

FIG. 9A is a photograph of blocks cut from Douglas fir studs treatedwith an antimicrobial wood preservative according to the presentinvention, and tested for mold growth (photo courtesy of the EarthScience Center, Faculty of Forestry, University of Toronto);

FIG. 9B is a photograph of untreated Southern yellow pine sapwood blockstested for mold growth (photo courtesy of the Earth Science Center,Faculty of Forestry, University of Toronto);

FIG. 10A is a chart showing the degree of mold growth on Southern yellowpine sapwood samples treated with an antimicrobial wood preservativeaccording to the present invention, treated with other products oruntreated (data courtesy of the Earth Science Center, Faculty ofForestry, University of Toronto); and

FIG. 10B is a photograph showing the degree of fungal growth on Southernyellow pine sapwood samples untreated or treated with an antimicrobialwood preservative according to the present invention or with acomparative formulation containing IPBC, IPBC and BCM, or PPCZ, at aconcentration of active ingredients of 900 μg/ml, and tested for moldgrowth (photo courtesy of the Earth Science Center, Faculty of Forestry,University of Toronto).

DETAILED DESCRIPTION

One aspect of the present invention provides an antimicrobialcomposition for use in protecting wood from attack by microbes such asfungi and bacteria. As used herein, the term “antimicrobial” is intendedto mean a compound or mixture of compounds, including but not limited toa microbicide or microbiocide, which is an agent effective to kill, orto reduce or prevent the growth of, or infection by, one or more livingmicroorganisms, including but not limited to bacteria and fungi. Anantimicrobial substance includes but is not limited to a bactericide,bacteriostat, or antibacterial substance, and a fungicide, fungistat orantifungal substance.

In at least one embodiment, the antimicrobial composition has a higherconcentration of active antimicrobial ingredients than the minimumnecessary for antimicrobial effectiveness. Thus, the antimicrobialcomposition can be diluted while still retaining antimicrobial efficacy.The antimicrobial composition is useful as an additive to water-basedwood coatings, so as to provide the wood coating with antimicrobialproperties and/or increase the antimicrobial effectiveness of the woodcoating. The antimicrobial composition can also be formulated as anantimicrobial wood preservative or an antimicrobial wood preservativeconcentrate as described below. The antimicrobial wood preservativeconcentrate can be diluted with water to prepare an antimicrobial woodpreservative formulation having a desired concentration of activeingredients.

In at least one embodiment, the antimicrobial composition is a stablewater-miscible suspoemulsion containing three active antimicrobialingredients: 3-iodo-2-propynyl N-butyl carbamate (IPBC), propiconazole(PPCZ) and carbendazim (BCM). In at least one embodiment, theantimicrobial composition has one or more of the following desirableproperties: stable, flowable, having low levels of volatile organiccompounds (VOC), low foaming, having low odor. In at least oneembodiment, the antimicrobial composition can be formulated intowater-based wood preservatives or water-based wood coatings.

The antimicrobial composition can be used for antimicrobial protectionof wood substrates, including but not limited to wood substrates whichare wet or at risk of being wet. Suitable wood substrates include butare not limited to green logs, freshly sawn lumber, dried solid wood,previously installed wood, engineered wood, and wood composite products,including but not limited to sheathing materials such as oriented strandboard (OSB) or plywood. Such antimicrobial protection can includeprevention of microbial infection of uninfected wood substrates andtreatment of sound wood substrates exposed to microbial infection fromwhich damaged, rotten or infected material has been mechanically orphysically removed. In at least one embodiment, the antimicrobialcomposition can be used for antimicrobial protection of new woodsubstrates prior to or immediately after installation. In at least oneembodiment, the antimicrobial composition can be used for in situantimicrobial protection of sound wood substrates in existinginstallations. In at least one embodiment, the antimicrobial compositioncan be used for remedial antimicrobial protection of sound woodsubstrates in existing installations where the sound wood substrate hasbeen attacked, or is at risk of being attacked, by microbes. Suchremedial protection can include mechanical or physical removal of fungalcolonies and removal and/or replacement of damaged, rotten or infectedwood substrate material in combination with application of theantimicrobial composition to sound and/or new wood substrate.

The present antimicrobial composition comprises from about 10% to about25% by weight of 3-iodo-2-propynyl N-butyl carbamate (IPBC), about 12%to about 20% by weight of propiconazole and about 2% to about 8% byweight of carbendazim, as active antimicrobial ingredients. In at leastone embodiment, the antimicrobial composition comprises from about 15%to about 20% by weight of IPBC, about 13% to about 17% by weight ofpropiconazole and about 3% to about 5% by weight of carbendazim. IPBChas the following structural formula:

Propiconazole (PPCZ), also known as1-((2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl)-methyl)-1H-1,2,4-triazole,has the following structural formula:

Carbendazim (BCM), also known as methyl benzimidazole-2-yl carbamate,has the following structural formula:

In at least one embodiment, the antimicrobial composition contains aratio by weight of IPBC:PPCZ:BCM of about 20:20:10. In at least oneembodiment, the antimicrobial composition contains a ratio by weight ofIPBC:PPCZ:BCM of about 19:19:5. In at least one embodiment, theantimicrobial composition contains a ratio by weight of IPBC:PPCZ:BCM ofabout 15:14:4. In at least one embodiment, the antimicrobial compositioncontains from about 24% to about 53% by weight of total activeantimicrobial ingredients (IPBC, PPCZ and BCM). In at least oneembodiment, the antimicrobial composition contains from about 32% toabout 40% by weight of total active antimicrobial ingredients.

In at least one embodiment, the IPBC and BCM are present in solid formand are dispersed in the antimicrobial composition as finite particles.In at least one embodiment, the particles have a particle size fromabout 0.1 μm to about 10 μm. In at least one embodiment, the particleshave a particle size from about 10 μm to about 35 μm. In at least oneembodiment, the particles have a particle size from about 13 μm to about20 μm.

In at least one embodiment, the antimicrobial composition furthercomprises an emulsion stabilizer. In at least one embodiment, theemulsion stabilizer is a natural or synthetic mineral, including but notlimited to clay-based minerals or clay mineral derivatives, such askaolin, Laponite™ RD or Laponite™ RDS (Rockwood Specialties), bentonite,or bentonite containing montmorillonite. Without being bound by theory,it is believed that the emulsion stabilizer aids in stabilizing theemulsion of the active ingredients in the antimicrobial composition. Theskilled person would be aware of other suitable emulsion stabilizers. Inat least one embodiment, the composition comprises from about 3% toabout 14% by weight of the emulsion stabilizer. In at least oneembodiment, the composition comprises from about 5% to about 12% byweight of the emulsion stabilizer.

In at least one embodiment, the antimicrobial composition furthercomprises an emulsifier. In at least one embodiment, the emulsifier is anon-ionic surfactant. In at least one embodiment, the non-ionicsurfactant is an ethoxylated castor oil. In at least one embodiment, theethoxylated castor oil contains 30 to 40 ethylene oxide units permolecule of castor oil. In at least one embodiment, the ethoxylatedcastor oil has a Hydrophilic-Lipophilic Balance (HLB) of about 10 toabout 14. In at least one embodiment, the non-ionic surfactant is T-DET™C-40 or T-DET™ BP-1 (Harcros Chemicals Inc.) or HCO-25 (EthoxChemicals). In at least one embodiment, the emulsifier is an ionicsurfactant. In at least one embodiment, the ionic surfactant is ananionic surfactant. In at least one embodiment, the anionic surfactantis E-Sperse™ 100 (Ethox Chemicals). The person of skill in the art wouldbe aware of other suitable emulsifiers.

In at least one embodiment, the antimicrobial composition comprisesabout 7% to about 15% by weight of the emulsifier. In at least oneembodiment, the antimicrobial composition comprises about 10% to about15% by weight of the emulsifier. In at least one embodiment, theantimicrobial composition comprises about 7% to about 12% by weight ofthe emulsifier. In at least one embodiment, the antimicrobialcomposition comprises about 10% by weight of the emulsifier.

In at least one embodiment, the antimicrobial composition furthercomprises about 2% to about 4% by weight of a co-emulsifier. In at leastone embodiment, the antimicrobial composition further comprises about 3%to about 3.5% by weight of a co-emulsifier. In at least one embodiment,the co-emulsifier comprises at least one non-ionic surfactant. In atleast one embodiment, the co-emulsifier comprises a plurality ofnon-ionic surfactants.

In at least one embodiment, the co-emulsifier comprises a firstnon-ionic surfactant having a low Hydrophilic-Lipophilic Balance (HLB).In at least one embodiment, the first non-ionic surfactant is relativelylipophilic and can favour the formation of water-in-oil emulsions.Suitable first non-ionic surfactants include but are not limited tosorbitan oleate, sorbitan monooleate, Span™ 80, Arlacel™ 80, andEmulsifier S80.

In at least one embodiment, the co-emulsifier further comprises a secondnon-ionic surfactant having a high HLB. In at least one embodiment, thesecond non-ionic surfactant is relatively hydrophilic and can favour theformation of oil-in-water emulsions. Suitable second non-ionicsurfactants include but are not limited to polyoxyethylene sorbitanoleate, polyoxyethylene sorbitan monooleate, Polysorbate 80, Tween™ 80,Canarcel™ TW 80, Atlox™ 1087, Alkest™ 80 and Crillet™ 4.

In at least one embodiment, the ratio by weight of the first non-ionicsurfactant to the second non-ionic surfactant is from about 90:10 toabout 80:20. In at least one embodiment, the ratio by weight of thefirst non-ionic surfactant to the second non-ionic surfactant is about90:10. In at least one embodiment, the ratio by weight of the firstnon-ionic surfactant to the second non-ionic surfactant is about 85:15.In at least one embodiment, the ratio by weight of the first non-ionicsurfactant to the second non-ionic surfactant is about 83:17. In atleast one embodiment, the co-emulsifier has a combined HLB of from about4 to about 10. In at least one embodiment, the co-emulsifier has acombined HLB of from about 6 to about 9. In at least one embodiment, theco-emulsifier has a combined HLB of from about 6 to about 7.

In at least one embodiment, the antimicrobial composition furthercomprises a carrier fluid. The carrier fluid is a water-miscible liquidand, in at least one embodiment, is selected from water, glycols andmixtures thereof. Suitable glycols include but are not limited toethylene glycol, diethylene glycol, triethylene glycol, propyleneglycol, dipropylene glycol, tripropylene glycol, and monoethers orpolyethers thereof. In at least one embodiment, the antimicrobialcomposition comprises from about 25% to about 70% by weight of thecarrier fluid, such that the solid content of the antimicrobialcomposition is about 30% to about 75% by weight. In at least oneembodiment, the antimicrobial composition comprises from about 35% toabout 65% by weight of the carrier fluid, such that the solid content ofthe antimicrobial composition is about 35% to about 65% by weight. In atleast one embodiment, the antimicrobial composition comprises from about45% to about 60% by weight of the carrier fluid, such that the solidcontent of the antimicrobial composition is about 40% to about 55% byweight.

In at least one embodiment, the antimicrobial composition furthercomprises a defoaming agent. In at least one embodiment the defoamingagent comprises at least one of silicones and paraffinic mineral oils.Suitable defoaming agents are well known to the skilled person and areavailable commercially from suppliers including but not limited to BYKAdditives and Instruments, Air Products, and the Dow Chemical Company.In at least one embodiment, the antimicrobial composition comprises fromabout 0.3% to about 3% by weight of the defoaming agent. In at least oneembodiment, the antimicrobial composition comprises from about 0.3% toabout 1% by weight of the defoaming agent.

In at least one embodiment, the antimicrobial composition is prepared byblending the components to form a stable emulsion, as will be understoodby one skilled in the art. In at least one embodiment, a mixture of IPBCand BCM, emulsifier, emulsion stabilizer, defoaming agent and water canbe emulsified and the resulting emulsion can be blended with a solutionof PPCZ in a glycol solvent. Alternatively, the co-emulsifier can beadded to the solution of PPCZ in a glycol solvent to form a pre-mix, andthe pre-mix can be incorporated into the emulsion containing the mixtureof IPBC and BCM. In at least one embodiment, the glycol solvent isdipropylene glycol monomethyl ether (DPM). In at least one embodiment,the ratio by weight of the emulsion of IPBC and BCM, emulsifier,emulsion stabilizer, defoaming agent and water to the solution of PPCZor to the pre-mix of the solution of PPCZ and the co-emulsifier is fromabout 76:24 to about 60:40.

In at least one embodiment, the mixture of IPBC and BCM, emulsifier,emulsion stabilizer, defoaming agent and water can contain about 25% toabout 40% by weight of the active antimicrobial ingredients, about 10%to about 20% by weight of the emulsifier, about 4% to about 23% byweight of the emulsion stabilizer, about 0.4% to about 5% by weight ofthe defoaming agent and about 40% to about 60% by weight of water. Insuch embodiments, the ratio of IPBC:BCM in the active microbialingredients can be from about 75:25 to about 85:15.

In at least one embodiment, the solution of PPCZ can be prepared bydiluting 95% to 100% by weight PPCZ (Wocosen™ 95%, Janssen PMP orPreventol™ A 12, Lanxess) with a glycol solvent at a ratio of about50:50 by weight. In at least one embodiment, the glycol solvent isdipropylene glycol monomethyl ether (DPM). In at least one embodiment, aco-emulsifier is added to the solution of PPCZ to form the pre-mix. Inat least one embodiment, a first non-ionic surfactant and a secondnon-ionic surfactant are added individually to the solution of PPCZ toform the pre-mix. In at least one embodiment, the pre-mix can containabout 7% to about 8% by weight of the first non-ionic surfactant, about1% to about 2% by weight of the second non-ionic surfactant and about43% to about 46% by weight PPCZ.

In at least one alternative embodiment, the antimicrobial composition isprepared by blending one or more pre-formed antimicrobial components,each containing one or more of the active antimicrobial ingredients. Inat least one embodiment, one or more of the pre-formed antimicrobialcomponents further contain one or more emulsion stabilizers, one or moreemulsifiers or one or more defoaming agents. One or more otheradditives, including but not limited to preservatives, anti-settlingagents, anticaking agents, pH stabilizers and rheology modifiers, canalso be present.

In at least one embodiment, the antimicrobial composition is preparedfrom a mixture of about 30% to about 50% by weight of an aqueousdispersion containing about 30-50% by weight IPBC and about 5-20% byweight kaolin, about 20% to about 35% by weight of an aqueous dispersioncontaining about 1-10% by weight IPBC, about 5-20% by weight kaolin andabout 10-20% by weight carbendazim, and about 24% to about 40% by weightof a solution containing about 45-50% by weight propiconazole in aglycol solvent. In at least one embodiment, the antimicrobialcomposition further contains about 3.0% to about 3.5% by weight of aco-emulsifier comprising a first non-ionic surfactant and a secondnon-ionic surfactant.

In at least one embodiment, the antimicrobial composition is preparedfrom a mixture of about 37% to about 42% by weight of an aqueousdispersion containing about 40% by weight IPBC and about 5-20% by weightkaolin (Polyphase™ PW 40, Troy Corporation), about 25% to about 30% byweight of an aqueous dispersion containing about 5% by weight IPBC,about 5-20% by weight kaolin and about 15% by weight carbendazim(Polyphase™ P678, Troy Corporation), about 2.2% to about 2.9% by weightof a first non-ionic surfactant (Span™ 80, Croda), about 0.3% to about0.7% by weight of a second non-ionic surfactant (Tween™ 80, Croda), andabout 29% to about 33% by weight of a technical concentrate containingabout 45-50% by weight propiconazole in a glycol solvent (Wocosen™ 50TK,Janssen PMP or Preventol™ A 12-TK 50, Lanxess), or a solution of PPCZprepared by diluting 95% to 100% by weight PPCZ (Wocosen™ 95%, JanssenPMP or Preventol™ A 12, Lanxess) with a glycol solvent at a ratio byweight of about 50:50, as described herein.

In at least one embodiment, about 57% to about 61% by weight ofPolyphase™ PW 40 and about 39% to about 43% by weight of Polyphase™ P678can be mixed together to form an emulsion. In at least one embodiment,about 90% to about 92% by weight of Preventol™ A 12-TK 50 or a solutionof PPCZ prepared by diluting Preventol™ A 12 with DPM at a ratio ofabout 50:50 can be mixed with about 7% to about 8% by weight of Span™ 80and about 1% to about 2% by weight of Tween™ 80 to form a pre-mix. In atleast one embodiment, about 32% to about 36% by weight of the premix canbe added to about 64% to about 68% by weight of the emulsion to form theantimicrobial composition.

The present antimicrobial composition can be diluted with water forapplication to freshly cut and undried (green) wood surfaces, includingbut not limited to green lumber or timber, rough cut logs and rough sawnbeams and planks. Such application can provide temporary protection tothe green wood surfaces during natural drying and before furthermachining. In at least one embodiment suitable for dilution with water,the present antimicrobial composition advantageously contains aco-emulsifier.

In at least one embodiment suitable for application to green woodsurfaces, the present antimicrobial composition can be diluted withwater at a ratio of antimicrobial composition to water of from about1:44 (v/v) to about 1:17 (v/v). In at least one embodiment, the ratio ofantimicrobial composition to water can be from about 1:37 (w/w) to about1:14 (w/w). In at least one embodiment, the diluted antimicrobialcomposition comprises from about 1.0% by weight of active ingredients toabout 2.5% by weight of active antimicrobial ingredients. The skilledperson will be able to determine and select a suitable dilution ratiofor a particular application depending on factors including but notlimited to the dimensions of the wood to be protected, the amount ofsapwood or heartwood, the initial moisture content of the wood, theenvironmental conditions under which the wood is stored, and the time ofnatural drying or exposure to seasoning. For example, large logs orbeams intended for construction of cabins or log homes and oftencontaining high proportions of sapwood may require application of adiluted antimicrobial composition containing a concentration of activeantimicrobial ingredients as high as 2.5% by weight to prevent attack bydeep penetrating blue stain fungi or surface-growing black and greenmold fungi which are hard to remove. As an additional example, thinnerrough sawn lumber intended for further cutting or shaping may beadequately protected by application of a diluted antimicrobialcomposition containing a concentration of active antimicrobialingredients as low as 1.0% by weight.

The present antimicrobial composition can be used in the preparation ofan antimicrobial wood preservative. In at least one embodiment, theantimicrobial composition can be formulated with one or more additivesto prepare an antimicrobial wood preservative concentrate, as will beunderstood by the skilled person. Suitable additives are well known inthe art and include but are not limited to carriers, resins, UVadditives to provide protection from UV-induced degradation,water-repellent additives and the like. In at least one embodiment, theantimicrobial composition can be incorporated into a pre-formed woodpreservative formulation, to prepare an antimicrobial wood preservativeor an antimicrobial wood preservative concentrate.

In at least one embodiment, the antimicrobial wood preservativeconcentrate contains about 3% to about 5% by weight of total activeantimicrobial ingredients (IPBC, PPCZ and BCM). In at least oneembodiment, the antimicrobial wood preservative concentrate can bediluted with water to prepare the antimicrobial wood preservative,which, in at least one embodiment, is suitable for application to a woodsurface to be preserved. In at least one embodiment, the ratio ofantimicrobial wood preservative concentrate to water in theantimicrobial wood preservative is from 1:4 to 1:25 by volume. In atleast one embodiment, the ratio of antimicrobial wood preservativeconcentrate to water is about 1:6 by volume. In at least one embodiment,the ratio of antimicrobial wood preservative concentrate to water isabout 1:9 by volume. The skilled person will be able to determine andselect a suitable dilution ratio depending on factors including but notlimited to the desired or required uptake of preservative into the woodto be treated, the conditions of use (including but not limited to theease with which the wood absorbs liquids, and the extent of directcontact of the wood with the ground), the seasonal conditions, theextent of exposure of the wood to moderate or harsh conditions,including but not limited to UV exposure, the risk of leaching of activeingredients and the risk of fungal attack to the wood to be treated.

The antimicrobial wood preservative can be applied to a wood surface tobe preserved by any application method known in the art, including butnot limited to spraying, dipping or immersion, flooding, orimpregnation. Dip or immersion treatments can be used to protect greenwood or dried construction elements, and include but are not limited todipping in dipping tanks for 1 to 5 minutes or immersion for 5 to 60seconds. Flood treatments can be used to protect construction andframing wood, shingles, sheathing and wood composite elements.Impregnation treatments include but are not limited to impregnation inhermetically closed treating vessels, including but not limited todouble vacuum treatment, vacuum-pressure-vacuum treatment and full-cellvacuum-pressure treatment. When impregnating wood in a hermeticallyclosed treating vessel, the wood can be treated with an antimicrobialwood preservative prepared by diluting the present antimicrobial woodpreservative concentrate with water at a ratio by volume of from about1:12 to about 1:25, such that about 3 kg to about 12 kg of dried activematerial is retained per m³ of wood. Double vacuum treatment can be usedto treat wood joinery, windows and doors. Vacuum-pressure-vacuumtreatment can be used to treat construction wood in ground contact.Full-cell vacuum-pressure treatment can be used to treat wood exposed toharsh conditions, in humid areas and/or in ground contact, such thatabout 7 kg to about 12 kg of dried active material is retained per m³ ofwood. The person skilled in the art will be able to select and carry outan appropriate application method for the specific conditions.

In at least one embodiment, the present antimicrobial composition can beincorporated into a compatible water-based wood coating to form anantimicrobial water-based wood coating product. Such water-basedcoatings are desirable for use because of their lower environmental andhealth risks, and the ease of cleaning of tools used to apply thecoating. It can be difficult to formulate such water-based wood coatingswith known antimicrobial compounds, which often have low solubility inwater, and therefore are difficult to mix effectively with water-basedcoatings. Because the present antimicrobial composition is awater-miscible stable emulsion of the active antimicrobial ingredients,it can be easier to formulate and can generally be more readily mixedwith water-based coatings.

As used herein, the term “compatible water-based wood coating” isintended to mean a water-based wood coating into which the antimicrobialcomposition can be incorporated, such that the resulting antimicrobialwood coating product is suitable for use in coating wood. The person ofskill in the art can readily determine the compatibility of theantimicrobial composition with other components in the water-basedcoating.

In use, incorporation of the antimicrobial composition into thecompatible water-based wood coating can take place at any convenientphase of the coating production process, including but not limited tothe grinding phase or the letdown phase. Alternatively, theantimicrobial composition can be added to the prepared compatiblewater-based coating once production is complete. In at least oneembodiment, the antimicrobial composition can be mixed with the woodcoating and the mixture agitated or stirred to form the antimicrobialwood coating product. In at least one embodiment, the mixture is stirredfor at least 5 minutes. In at least one embodiment, the wood coating isstirred or agitated prior to addition of the antimicrobial composition,and the antimicrobial composition is mixed with the wood coating in theletdown phase.

In at least one embodiment, the antimicrobial wood coating productcomprises from about 0.25% to about 2.50% by weight of the antimicrobialcomposition. Such embodiments of the antimicrobial wood coating productcan comprise from about 0.06% to about 1.2% by weight of total activeantimicrobial ingredients. In at least one embodiment, the antimicrobialwood coating product can comprise from about 0.09% to about 1.0% byweight of total active antimicrobial ingredients.

In at least one embodiment, the antimicrobial wood coating productcomprises from about 0.25% to about 1.00% by weight of the antimicrobialcomposition. Such embodiments of the antimicrobial wood coating productare useful for application to wood surfaces in interior locations. In atleast one embodiment, the antimicrobial wood coating product comprisesfrom about 1.00% to about 2.50% by weight of the antimicrobialcomposition. Such embodiments of the antimicrobial wood coating productare useful for application to wood surfaces in exterior locations. In atleast one embodiment, the antimicrobial wood coating product comprisesabout 0.25%, about 0.50%, about 1.00%, about 1.50%, about 2.00% or about2.50% by weight of the antimicrobial composition. The antimicrobial woodcoating product can be applied to a wood surface by any applicationmethod known to the skilled person.

In at least one embodiment, the present antimicrobial composition hasantifungal or fungicidal properties, and can be used to prepare afungicidal wood preservative or a fungicidal wood coating product, asdescribed herein. In such embodiments, the fungicidal wood preservativeor wood coating product is effective to kill, or to prevent or reducegrowth of or infection by, one or more fungi which infect, damage orotherwise attack wood. Such fungi include but are not limited to surfacemolds, blue stain fungi and wood rotting fungi. In at least oneembodiment, the fungicidal wood preservative or wood coating product iseffective to kill, or to prevent or reduce growth of or infection by, aplurality of fungi which attack wood. In such embodiments, thefungicidal wood preservative or wood coating product can have broadspectrum activity against a range of wood attacking fungi.

Non-limiting examples of wood attacking fungi which can be killed orcontrolled by antimicrobial wood preservatives and/or wood coatingproducts containing the present antimicrobial composition include wooddiscoloring organisms, deep penetrating wood staining fungi and surfacegrowing mold fungi, including but not limited to Ceratocystis pilifera,Aureobasidium pullulans, Aspergillus niger, Sclerophoma pityophila,Trichoderma viride, Penicillium citrinum, Alternaria alternate,Alternaria tenuissima, Cladosporium cladosporioides, Cladosporiumherbarum, Chaetomium globosum, Stachybotrys chartarum, and Stachybotrysatra; and wood destroying fungi, including white and brown rot species,including but not limited to Coniophora puteana, Coniophora cerebella,Postia placenta, Serpula lacrymans, Gloeophyllum trabeum, Trametesversicolor, Pleurotus ostreatus, and Stereum hirsutum.

In at least one embodiment, the present antimicrobial composition showsan increased efficacy against one or more species of microorganisms,including but not limited to one or more species of fungi, compared tothe efficacy shown by comparable formulations containing one or two ofthe individual active antimicrobial ingredients, IPBC, BCM or PPCZ,alone. In at least one embodiment, the present antimicrobial compositionshows an increased efficacy against one or more fungal species comparedto the efficacy shown by a comparable formulation of IPBC alone. In atleast one embodiment, the present antimicrobial composition shows anincreased efficacy against one or more fungal species compared to theefficacy shown by a comparable formulation of IPBC and BCM alone. In atleast one embodiment, the present antimicrobial composition shows anincreased efficacy against one or more fungal species compared to theefficacy shown by a comparable formulation of PPCZ alone.

Without being bound by theory, it is believed that when at least oneembodiment of an antimicrobial wood coating product containing thepresent antimicrobial composition is applied to a wood surface, theactive ingredients can migrate into the wood cells near the surface,preventing microorganisms from growing on the coating film or on thesurface of the wood under the coating film. The growth of thesemicroorganisms, while not necessarily causing decay or structural damageto the wood, can cause an unsightly “blotchy” appearance below thecoating film, which can considerably reduce the commercial value of thewooden structure. In addition, the adhesion of the coating to the woodcan be compromised by the microbial growth such that, in some cases, thecoating can peel away from the wood. With reference to FIG. 1, it isbelieved that when at least one embodiment of a wood coating 12containing the present antimicrobial composition is applied to wood 10,the antimicrobial components can penetrate into the wood for somedistance (about 0.5 mm to about 2 mm) before the coating film dries.This is believed to provide a protective zone 14 under coating 12, whichprovides added protection to the coated surface. Thus, even if theuncoated side or rear surfaces 16 of the wood are invaded by woodstaining fungi, the coated surface of the wood is protected fromdiscoloration and peeling away of the coating. Such wood staining fungiinclude but are not limited to species such as Aureobasidium pullulans,which may not cause decay or loss of mechanical strength in the wood,but can cause unsightly discoloration and loss of adhesion of thecoating.

In at least one embodiment, the antimicrobial composition canadvantageously prevent or reduce bacterial contamination of awater-based wood coating to which the antimicrobial composition isadded, thus providing an antimicrobial wood coating product withimproved storage time without the need for additional in-canpreservatives. Bacteria growing in water-based wood coatings orpreservatives can cause problems such as unpleasant or offensive odours,reduction of solid content, a decrease in adhesion of the dried filmafter application, and degradation of antifungal compounds, withconsequent loss of antifungal efficacy. Thus, the antimicrobial woodcoating product, in at least one embodiment, can be stored for a longerperiod of time with reduced or minimal bacterial contamination than acomparable water-based wood coating which does not contain the presentantimicrobial composition. Antimicrobial wood coating productscontaining the present antimicrobial composition have been found to showno detectable bacterial growth after extended storage for up to 12months under normal ambient and increased (for example, 32° C.)temperatures.

EXAMPLES

Other features of the present invention will become apparent from thefollowing non-limiting examples which illustrate, by way of example, theprinciples of the invention.

Example 1

An antimicrobial composition according to the present invention wasincorporated into a water-repellent, UV resistant wood preservativeformulation to provide an antimicrobial wood preservative concentratecomprising 3.33% by weight of active antimicrobial ingredients (IPBC,BCM and PPCZ). A negligible amount of blue pigment was added tofacilitate visualization of treated surfaces. The concentrate wassubsequently diluted with water at ratios of 6:1, 9:1 and 25:1(water:concentrate, v/v) to provide test formulations A, B and C,respectively.

Five-inch sapwood sections cut from lodgepole pine 2″×4″ studs(Shelburne Wood Protection Ltd.) were end-sealed to prevent longitudinalpenetration, immersed for 10 seconds in one of test formulations A, B orC and allowed to dry for 10 days under ambient conditions (21° C., 50%relative humidity). The sealed ends of the blocks were cut-removed toexpose untreated surfaces as a control, and the blocks were exposed tomold species (Aureobasidium pullulans ATCC (American Type CultureCollection) 9348; Aspergillus niger ATCC 6275 and Penicillium sp ATCC9849) for 12 weeks in a humidity chamber under a controlled environment(28° C.-32° C., 95%-98% relative humidity) as described in ASTM StandardD3273-12 (2012), Standard Test Method for Resistance to Growth of Moldon the Surface of Interior Coatings in an Environmental chamber, ASTMInternational, West Conshohocken, Pa. Three replicate samples weretreated with each test formulation. The results are presented in Table 1below.

TABLE 1 Concentration Preservative Average of absorption mold active(retention growth Test Dilution ingredients of actives) on woodformulation ratio (%, w/w) (g/m²) surfaces (%) A  6:1 0.476 118 (0.562)0 B  9:1 0.333 123 (0.409) 0 C 25:1 0.128 127 (0.163) 0 untreated N/AN/A 0.00 50

As seen in FIG. 2, no mold growth was observed on the treated surfaces,even those treated with the most dilute formulation C, while theuntreated exposed surface was intensively colonized by mold. Somediscoloration of the treated wood was observed due to chemicalreactions, and was not the result of fungal attack.

Example 2

An independent comparative test of mold control products from Canadiansuppliers, including the test formulation A described in Example 1 above(Product A), was carried out, at the request of a Canadian provincialgovernment agency (BC Housing Homeowner Protection Office), to identifyproducts from a variety of manufacturers which might be useful forpreventing mold growth on wood roof sheathing in ventilated attics ofwood frame structures in British Columbia. As seen in FIG. 3,unprotected attics in this region are susceptible to attack by moldfungi.

The test was carried out according to AWPA Standard E24-12 (StandardMethod of Evaluating the Resistance of Wood Product Surfaces to MoldGrowth; published May 1, 2012 by American Wood Protection Association).The identities of the products tested were kept confidential, and madeknown only to their particular manufacturers.

Test samples of Douglas fir plywood sheets with one side ofsapwood-predominant veneer, having dimensions of 160 mm×65 mm×10 mm,were treated with each product according to manufacturer'sspecifications. In the case of present Product A, 20 test samples wereimmersed vertically for 5 seconds, removed, turned upside down andimmersed again for an additional 5 seconds, then allowed to dry for atleast 10 days. The 10 samples with the most similar uptake were selectedfor use in the test. The average uptake of Product A was 137 g/m², withan average uptake of active antimicrobial ingredients of 0.65 g/m².Uptake values for other products tested (unidentified) varied from 106to 259 g/m². Samples were subjected to the test conditions described inAWPA Standard E24-12, and were randomly assigned to locations in thetest chamber. Fungal inocula contained five common mold organisms,namely Alternaria tenuissima (Forintec 691B); Aspergillus niger(Forintec 207F); Aureobasidium pullulans (Forintec 132F); Penicilliumcitrinum (Forintec 595F); and Cladosporium cladosporioides (Forintec273C). Mold growth was monitored and reported at 2, 4, 6 and 8 weeks.Samples were rated for mold growth on a scale 0 to 5 where 0 representsno growth and 5 represents intensive fungal growth. The results areprovided in Table 2 below.

TABLE 2 Mold growth rating 2 weeks 4 weeks 6 weeks 8 weeks AverageAverage Average Average (standard Range (standard Range (standard Range(standard Range Product deviation) (max-min) deviation) (max-min)deviation) (max-min) deviation) (max-min)  1 0.0 (0)   0-0 0.8 (0.8) 2-02.3 (1.3) 4-1 3.0 (0.8) 4-2  2 0.2 (0.4) 1-0 3.6 (0.7) 4-2 4.0 (0)   4-44.0 (0)   4-4  3 0.1 (0.3) 1-0 0.4 (0.5) 1-0 1.1 (1.0) 3-0 2.3 (1.2) 4-1 4 0.0 (0)   0-0 0.9 (0.7) 2-0 3.1 (1.0) 4-1 3.8 (0.4) 4-3  5 0.0 (0)  0-0 1.1 (0.6) 2-0 3.1 (0.9) 4-2 4.0 (0.5) 5-3  6 0.1 (0.3) 1-0 0.1 (0.3)1-0 1.0 (0.5) 2-0 2.4 (0.7) 3-1 (Product A)  7 0.0 (0)   0-0 0.6 (0.5)1-0 2.7 (0.7) 4-2 3.8 (0.4) 4-3  8 0.0 (0.3) 1-0 2.4 (1.1) 4-1 4.0 (0)  4-4 4.0 (0)   4-4  9 0.4 (0.5) 1-0 3.7 (0.7) 4-2 4.0 (0)   4-4 4.2 (0.4)5-4 10 0.0 (0)   0-0 0.0 (0)   0-0 0.1 (0.3) 1-0 0.1 (0.3) 1-0

As seen from the results in Table 2, Product A (table entry 6) showedexcellent control of mold growth under the test conditions, and wasidentified along with the product of table entry 3 (unidentified) asproviding the best resistance to mold growth among the products tested.The product of table entry 10 is a non-commercial 100% concentratedmulti-active formulation developed by the independent organizationconducting the test (FPlnnovations, Vancouver, BC, Canada), and wasincluded as a positive control.

The three commercial products which provided the best resistance to moldgrowth in the test above (table entries 1, 3 and 6 (Product A)) werefurther tested under modified conditions which incorporate intermittentvapour condensation on sample surfaces to better represent theconditions typically found in attics in the Lower Mainland of BritishColumbia. Ten test samples were prepared as described above, and thefive samples with the most similar uptake were selected for use in thetest. The average uptake of Product A was 141.2 g/m², while the averageuptake of table entries 1 and 3 were 154.6 g/m² and 113.2 g/m²,respectively. Fungal inocula were as described above.

The conditions and apparatus described in AWPA Standard E24-12 wereused, with some modification. The treated samples were placed in holescut in an insulated flat roof, rather than being suspended inside thechamber, so that the sapwood-predominant veneer test face of the samplewas exposed to the interior of the chamber and the other face wasexposed to the outside of the chamber. The interior of the chamber wasmaintained at 100% humidity and 25° C., and the air outside the chamberwas conditioned to 16° C. to 20° C., so that condensation on the testsamples was promoted. A fan installed in the chamber could be operatedto blow air from the chamber outwards through an 8 cm by 9 cm hole inthe chamber wall, and a similar hole at the other end of the chamberallowed entry of air from outside the chamber while the fan wasoperating. When the fan was not operating, plastic hinged flapsprevented air from entering or leaving the chamber.

The test samples were exposed to a cycle including a condensation periodof three days and a drying period of four days to provide an acceleratedsimulation of attic conditions. The condensation period included arepeated cycle of a 30 minute chamber condition of about 26° C. and 96%relative humidity, followed by a 30 minute period where cooler room airwas introduced into the chamber by means of the fan, to provide achamber condition of about 22° C. and 75% relative humidity. With entryof cooler air, water inside the chamber was heated to raise thetemperature inside the chamber to 26° C. once operation of the fan wasdiscontinued. When the three day condensation period had ended, theheater and fan were turned off to allow the chamber to slowlyequilibrate to ambient temperature (about 20° C. to 22° C.) and about80% to 90% relative humidity over the four day drying period.

Mold growth on test samples was observed at 2, 4, 6, 8 and 12 weeks ofexposure, and rated as follows:

-   -   0 No visible growth;    -   1 Mold covering up to 10% of surfaces, providing growth is not        so intense or colored as to obscure the sample color over more        than 5% of surfaces;    -   2 Mold covering between 10% and 30% of surfaces, providing        growth is not so intense or colored as to obscure the sample        color over more than 10% of surfaces;    -   3 Mold covering between 30% and 70% of surfaces, providing        growth is not so intense or colored as to obscure the sample        color over more than 30% of surfaces;    -   4 Mold on greater than 70% of surfaces, providing growth is not        so intense or colored as to obscure the sample color over more        than 70% of surfaces;    -   5 Mold covering 100% of surfaces or with less than 100% coverage        and with intense or colored growth obscuring greater than 70% of        the sample color.

The results are presented in Table 3 below, and in FIG. 4.

TABLE 3 2 Weeks 4 Weeks 6 Weeks 8 Weeks 12 Weeks Test Avg* Avg* Avg*Avg* Avg* sample (SD) Max-min (SD) Max-min (SD) Max-min (SD) Max-min(SD) Max-min Positive 4.0 5-3 4.8 5-4 4.8 5-4 4.8 5-4 5.0 5-5 control(0.7) (0.4) (0.4) (0.4) (0.0) (untreated Douglas fir plywood) Positive1.6 4-0 1.6 4-0 1.6 4-0 2.0 4-0 2.6 5-0 control (1.8) (1.8) (1.8) (1.9(2.1) (untreated Ponderosapine sapwood) Entry 1 0.0 0-0 0.2 1-0 0.2 1-00.8 3-0 1.4 3.0 (0.0) (0.4) (0.4) (1.3) (1.5) Entry 3 0.6 2-0 0.2 1-00.2 1-0 0.0 0-0 0.0 0-0 (0.9) (0.4) (0.4) (0.0) (0.0) Entry 6 0.0 0-00.0 0-0 0.0 0-0 0.0 0-0 0.0 0-0 (Product A) (0.0) (0.0) (0.0) (0.0)(0.0) *Average (standard deviation); average of 5 replicates

As seen from the data in Table 3 and FIG. 4, Product A (entry 6 of Table2) provided the best control of mold growth of the three productstested, and prevented mold growth under the test conditions for at least12 weeks.

Example 3

An antimicrobial composition according to the present invention wasincorporated into a wood preservative formulation to provide anantimicrobial wood preservative concentrate comprising 3.33% by weightof active antimicrobial ingredients (IPBC, BCM and PPCZ). Theconcentrate was diluted with water at a ratio of 12:1(water:formulation, v/v), to provide test formulation D, containing0.26% of active antimicrobial ingredients. Comparative formulation Econtaining 0.26% of IPBC was prepared similarly.

White pine sapwood blocks (20 mm×10 mm×6 mm) were immersed for 5 secondsin test formulation D or in the comparative formulation E, and wereallowed to dry without contacting each other for 10 days undercontrolled laboratory conditions (21° C., 40-50% relative humidity). Thetreated blocks were sterilized by passing briefly through an alcoholbased burner flame, and were placed directly on sterile Difco™ culturemedium containing 3.5% malt extract agar in plastic culture dishes (100mm in diameter, 20 mm in height; 5 replicates each).

The culture medium was inoculated as close to the dish edge as possiblewith two inocula (approximately 10 mm×10 mm fragments) of each of threedecay fungi, namely Gloeophyllum trabeum GT RR-5 (brown rot fungus),Postia placenta (brown rot fungus) and Trametes versicolor (white rotfungus) (6 inocula in total per plate). Gloeophyllum trabeum GT RR-5 wasinitially isolated from a naturally infected log placed out of groundcontact, and the culture was purified by multiple mycelia transfer usingbeer-based medium (Sansin) containing 3% malt extract, 2% agar and 0.3%food-grade 35% hydrogen peroxide (H₂O₂). Postia placenta and Trametesversicolor are isolates obtained from the Faculty of Forestry,University of Toronto. Poor growth of Trametes versicolor mats isbelieved to result from contamination of the originally acquiredculture. Formation of fungal colonies was observed for four weeks.

No wood blocks were observed to be colonized by fungal mycelia. Typicalresults are seen in FIG. 5, in which sample 16 (right), which wastreated with test formulation D, shows a larger zone of growthinhibition than does sample 40 (left), which was treated with IPBC alone(comparative formulation E). Average growth inhibition zones weremeasured at 1 to 12 mm for the blocks treated with IPBC alone(comparative formulation E) and 7 to 15 mm for test formulation D.Gloeophyllum trabeum appeared to be the most tolerant of the threespecies tested to the antifungal effects of both test formulation D andIPBC alone.

Example 4

An antimicrobial composition according to the present invention wasincorporated into an alkyd-based, water-dilutable, clear decorative woodstain to provide an antimicrobial wood coating formulation containing0.28% by weight of active antimicrobial ingredients (IPBC, BCM and PPCZ)(formulation F). A comparable wood coating formulation was preparedcontaining 0.28% of IPBC alone (formulation G). White pine sapwoodblocks (50 mm×25 mm×15 mm) were individually dip treated for 5 secondswith formulation F or formulation G, dried for 2 days and acclimatizedfor 7 days at 80% humidity. The thickness of the dry film on coatedsurfaces was measured at 1 to 1.3 mils.

The blocks were sterilized by promptly passing the blocks over analcohol burner flame. Ten replicate culture plates were prepared byplacing a block treated with formulation F, a block treated withformulation G and a control untreated block on sterile 2 cm×2 cm plasticsupports in each of ten plastic culture dishes (100 mm in diameter, 20mm in height) containing sterile Difco™ culture medium comprising 3%malt extract agar. The dishes were aseptically sprayed with either aspore suspension containing a blend of spores of Aspergillus niger(strain ATTC 6275) and Penicillium funiculosum (strain ATTC 11797), orwith a spore suspension containing spores of Aureobasidium pullulans(strain ATTC 9348). The plates were incubated at 28° C. for four weeksand the growth of fungal mycelia was rated as follows:

-   -   0—No growth;    -   1—Traces of growth (up to 10% visible surface overgrown);    -   2—Light growth (10 to 30% visible surface covered);    -   3—Moderate growth (30 to 60% visible surface covered);    -   4—Heavy growth (more than 60% covered to complete coverage).        The results are presented in Table 4 and typical results are        shown in FIG. 6.

TABLE 4 Fungal Growth Ratings: Formulation F Formulation G Controlsample (IPBC, PPCZ, Dish number (IPBC) (untreated) BCM) Dishes sprayedwith A. pullulans spore suspension 1 0 1 0 2 1 1 0 3 0 2 0 4 0 1 0 5 1 20 Dishes sprayed with A. niger and P. funiculosum spore suspension 6 0 30 7 1 3 0 8 1 3 0 9 3 4 0 10 0 2 0

As can be seen from FIG. 6 (photograph taken with the lid removed fromthe culture dish), the block coated with formulation F (left, indicatedas “9 P-7257”) showed no mold growth, the block coated with the coatingcontaining IPBC alone (formulation G, right, indicated as “9A CLO”)showed limited mold growth, and the untreated control block (FIG. 6,center, unmarked) showed significant mold growth.

Example 5

Wood preservative formulations containing an antimicrobial compositionaccording to the present invention were tested (at the Earth ScienceCenter, Faculty of Forestry, University of Toronto) for resistance towood decay fungi by the NWWDA standard Soil Block Test Method (NWWDAStandard TM1:1994 (R2006) (1994, renewed 2006), National Wood Window andDoor Association). An antimicrobial composition according to the presentinvention was incorporated into a ready to use wood preservativeformulation to provide an antimicrobial wood preservative formulationcomprising 0.46% by weight of active antimicrobial ingredients (IPBC,BCM and PPCZ) (formulation H). Formulation H was diluted 5.4 times withwater to provide formulation I, containing 0.085% active antimicrobialingredients (IPBC, BCM and PPCZ).

Formulation H and formulation I were applied to 19 mm blocks of red pinesapwood and poplar sapwood and the blocks were vacuum treated for 30minutes as described in section 9 of the NWWDA standard method. Theaverage retention (six replicates) for the treated red pine sapwoodblocks was 1.8 kg/m³ (for blocks treated with formulation H) and 0.31kg/m³ (for blocks treated with formulation I), and, for the treatedpoplar sapwood blocks, the average retention was 1.5 kg/m³ (for blockstreated with formulation H) and 0.29 kg/m³ (for blocks treated withformulation I). A set of treated red pine sapwood blocks were exposed toaccelerated leaching as described in Method B of the NWWDA standardmethod. Untreated blocks were used as a control and each test wascarried out with six replicate blocks.

After conditioning and weighing, the test blocks were sterilizedovernight by exposure to UV light and were placed in glass jars onfeeder strips pre-inoculated with brown rot fungus (Gloeophyllumtrabeum) (red pine sapwood blocks) or white rot fungus (Trametesversicolor) (poplar sapwood blocks). The blocks were incubated for 12weeks, then re-equilibrated and weighed. The results are shown in Table5.

TABLE 5 Formu- Active Weight Standard Test fungus lation (%, w/w)Leaching loss (%) deviation Brown rot H 0.46 Non-leached −0.1 1.0 fungusH 0.46 Leached 0.6 0.7 (Gloeophyllum I 0.085 Non-leached 5.8 2.7trabeum) I 0.085 Leached 2.9 0.3 (red pine Untreated 0 Non-leached 38.67.8 sapwood) White rot H 0.46 Non-leached 0.1 1.0 fungus I 0.085Non-leached 22.9 10.8 (Trametes Untreated 0 Non-leached 46.0 10.4versicolor) (poplar sapwood)

As seen from the results in Table 5, untreated (control) red pinesapwood blocks had a significant average weight loss of 38.6% due todecomposition caused by Gloeophillum trabeum. However, treated red pinesapwood blocks showed minimal weight loss when treated with eitherformulation H or formulation I. Even after leaching, minimal weight losswas observed, indicating that the active ingredients were well retained.In addition, as seen in FIG. 7, a block (blue, right) treated withformulation I and exposed to Gloeophillum trabeum for 12 weeks showedminimal colonization, even when exposed to fungal mycelia directlyplaced on top of the block. An untreated control block (left) showedextensive colonization.

In addition, untreated poplar sapwood blocks also showed significantweight loss of 46% when exposed to Trametes versicolor. However, poplarsapwood samples treated with formulation H lost only 0.1% of theirinitial weights. Poplar wood samples treated with formulation I showed aweight loss of 22.9%.

Example 6

The experiment was carried out at the Earth Science Center, Faculty ofForestry, University of Toronto. Formulation H (Example 5) was appliedto twelve (25 mm×25 mm×25 mm) red pine sapwood cubes using a 30-minutevacuum treatment at a pressure of 100 mm Hg, according to the NWWDAstandard Soil Block Test Method (NWWDA Standard TM1:1994 (R2006) (1994,renewed 2006), National Wood Window and Door Association). The blockswere dried for two weeks under ambient laboratory conditions and placedindividually in small beakers. Six of the blocks were loaded withweights and subjected to leaching by immersion in distilled water(approximately nine times the volume of the block samples) at roomtemperature for two hours and drying overnight at 49° C., repeated dailyfor 14 days. Three of the six leached blocks and three of the sixunleached blocks were precisely cut-dissected along a longitudinaldirection at 5 mm increments. The remaining three of the six leachedblocks and three of the six unleached blocks were preciselycut-dissected along a radial direction at 5 mm increments. All sectionswere individually ground to 30 mesh particle size and extracted withmethanol in an ultrasonic bath for 3 hours. The methanol extracts wereanalyzed for presence of actives (IPBC, PPCZ and BCM) using highperformance liquid chromatography (HPLC), at a limit of quantificationof 0.02 μg/ml. The results (average of three replicates per treatment)are presented in Table 6 and in FIGS. 8A and 8B.

TABLE 6 Block Retention of Actives Sample section (mm) Leachingμg/g_(wood) % Radial sections 1-NL 0-5 Non-leached 3,295 0.33 2-NL  5-10Non-leached 1,277 0.13 3-NL 10-15 Non-leached 376 0.04 4-NL 15-20Non-leached 1,744 0.17 5-NL 20-25 Non-leached 2,328 0.23 1-L 0-5 Leached3,473 0.35 2-L  5-10 Leached 997 0.10 3-L 10-15 Leached 694 0.07 4-L15-20 Leached 1,464 0.15 5-L 20-25 Leached 2,850 0.29 Longitudinalsections 1-NL 0-5 Non-leached 7,417 0.74 2-NL  5-10 Non-leached 656 0.073-NL 10-15 Non-leached 286 0.03 4-NL 15-20 Non-leached 524 0.05 5-NL20-25 Non-leached 5,241 0.52 1-L 0-5 Leached 6,844 0.68 2-L  5-10Leached 453 0.05 3-L 10-15 Leached 531 0.05 4-L 15-20 Leached 975 0.105-L 20-25 Leached 4,303 0.43

As can be seen from the results in Table 6 and FIGS. 8A and 8B, nosignificant loss of active ingredients was observed from the leachedblocks compared to the non-leached blocks.

Example 7

Wooden 2×4 studs (Douglas fir, 8 feet in length, green or kiln dried)were flood treated in a test retort by a commercial wood preservationcompany under industrial conditions with test formulations A, B, C andD, prepared by diluting the antimicrobial wood preservative concentrateof Example 1 comprising 3.33% by weight of active antimicrobialingredients (IPBC, BCM and PPCZ) with water at ratios of 6:1, 9:1, 25:1and 12:1, respectively (Examples 1 and 3). Five-inch long samples cutfrom the treated studs were tested for mold resistance using the AWPAE24-2012 test method (Example 2), along with untreated control samplesof Southern yellow pine sapwood or black or white spruce. The sampleswere continuously exposed to mold species for 8 weeks at 95% relativehumidity and temperatures of 28° C. to 32° C. Mold growth was visuallyassessed and recorded at 2, 4, 6 and 8 weeks exposure time, and wasrated as follows:

-   -   0 No visible growth;    -   1 Mold covering up to 10% of surfaces, with mild mycelia        density, obscuring hardly 5% surface;    -   2 Mold covering between 10-30% of surfaces, with mild mycelia        density, obscuring up to 10% surface;    -   3 Mold covering between 30-70% of surfaces, with medium mycelia        density, obscuring up to 30% surface;    -   4 Mold covering greater than 70% of surfaces, with intense        mycelia density, obscuring up to 70% surface;    -   5 Mold covering 100% of surface with intense discoloration,        obscuring more than 70% surface.

The results are presented in Table 7.

TABLE 7 Test Percentage Ratings Sample Wood Species Formulation ofsapwood Two Four Six Eight number and Treatment (dilution) (%) WeeksWeeks Weeks Weeks I-19 Southern Untreated 100 3 3 4 5 I-20 yellow pinecontrol 100 3 4 5 5 I-21 sapwood 100 3 3 4 5 Average (standarddeviation) 3.0 (0.0) 3.3 (0.6) 4.3 (0.6) 5.0 (0.0) II-15 Black SpruceUntreated Unknown 0 0 1 1 II-16 control Unknown 0 0 1 1 II-17 WhiteSpruce Untreated Unknown 0 0 2 3 II-18 control Unknown 1 1 2 4 Average(standard deviation) 0.3 (0.5) 0.3 (0.5) 1.5 (0.6) 2.3 (1.5) III-1DouglasFir A (6:1) 3 0 0 0 0 III-2 (green) 3 0 0 0 0 III-3 DouglasFir 500 0 0 0 III-4 (kiln dried) 50 0 0 0 0 Average (standard deviation) 0.0(0.0) 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) IV-5 DouglasFir B (9:1) 60 0 0 2 2IV-6 (green) 60 0 0 3 3 IV-7 DouglasFir 5 0 0 2 2 IV-8 (kiln dried) 5 00 1 1 Average (standard deviation) 0.0 (0.0) 0.0 (0.0) 2.0 (0.8) 2.0(0.8) V-9 Douglas Fir D (12:1) 0 0 0 0 0 V-10 (green) 0 0 0 0 0 V-11Douglas fir 60 0 0 1 1 (kiln dried) Average (standard deviation) 0.0(0.0) 0.0 (0.0) 0.3 (0.6) 0.3 (0.6) VI-12 Douglas Fir C (25:1) 0 0 0 0 0VI-13 (green) 0 0 0 0 0 VI-14 Douglas fir 2 0 0 0 0 (kiln dried) Average(standard deviation) 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) 0.0 (0.0)

As seen from the results in Table 7 and as shown in FIG. 9A, testformulation A, containing the antimicrobial wood preservativeconcentrate at a dilution ratio of 6:1, protected treated stud sampleshaving up to 50% sapwood content completely from mold colonization overan exposure period of 8 weeks. In contrast, as seen in FIG. 9B,untreated Southern yellow pine sapwood blocks were extensively colonizedby mold under the same conditions. As well, the present antimicrobialwood preservative concentrate showed moderate to good protection, evenat a dilution of 12:1, against mold growth in studs containing up to 60%sapwood over an exposure period of 8 weeks. The stud samples treatedwith test formulation C (containing the antimicrobial wood preservativeconcentrate at a 25:1 dilution ratio) showed no mold growth, butcontained a very high percentage of heartwood, which is more naturallyresistant to mold infection than is sapwood.

Example 8

The minimum inhibitory concentration (MIC) of total active ingredients(IPBC, PPCZ and BCM) in an antimicrobial composition according to thepresent invention (test formulation J) against a number ofwood-discoloring or wood-destroying fungi was determined using theSpiral Plater method as known in the art and compared against the MIC oftotal active ingredients in comparative formulations containing onlyIPBC (comparative formulation K, Polyphase™ PW 40, Troy Corporation) ora mixture of IPBC and BCM (1:3 ratio by weight, comparative formulationL, Polyphase™ P678, Troy Corporation). The results are shown in Table 8.

TABLE 8 Test Formulation J Comparative Comparative (IPBC, Formulation KFormulation L Fungus PPCZ, BCM) (IPBC) (IPBC, BCM) Mold(wood-discolouring) fungi Cladosporium <17 ppm <19 ppm 24 ppmcladosporioides (ATCC #16022) Aspergillus niger <17 ppm <19 ppm 34 ppm(ATCC #6275) Trichoderma viride <17 ppm <19 ppm <7 ppm (ATCC #20476)Wood rotting fungi Gloeophyllum <17 ppm <19 ppm <7 ppm trabeum (ATCC#11539) Postia placenta <17 ppm <19 ppm <7 ppm (ATCC #36334) Coniophoraputeana <17 ppm <19 ppm 43 ppm (ATCC #36336) Trametes versicolor <17 ppm<19 ppm 43 ppm (ATCC #42462)

As seen from the results presented in Table 8, the present antimicrobialcomposition exhibited MIC values against the fungi tested which are atleast comparable to those of comparative formulations K and L, andexhibited MIC values against two commercially important black moldspecies (Cladosporium cladosporioides and Aspergillus niger) and twodecay fungi (Coniophora puteana and Trametes versicolor) which aresuperior to those of comparative formulation L.

Example 9

The experiment was carried out at the Earth Science Center, Faculty ofForestry, University of Toronto. An antimicrobial composition accordingto the present invention was incorporated into a water-repellent, UVresistant wood preservative formulation to provide an antimicrobial woodpreservative concentrate comprising 3.33% by weight of activeantimicrobial ingredients (IPBC, BCM and PPCZ, Example 1). Theconcentrate was subsequently diluted with water at a ratio of 6:1(water:concentrate, v/v) to provide test formulation M containing 0.476%by weight of total active ingredients (IPBC, PPCZ and BCM). The biocidalproperties of test formulation M were compared to those of comparativeformulation N (similar to test formulation M but containing 0.476% byweight of IPBC only), comparative formulation O (similar to testformulation M but containing 0.476% by weight of a mixture of IPBC andBCM at a 1:3 ratio by weight) and comparative formulation P (similar totest formulation M but containing 0.476% by weight of PPCZ only). Eachof formulations M, N, O and P was further diluted with water to providetest solutions containing 900 μg/mL, 500 μg/mL, 250 μg/mL, 100 μg/mL, 50μg/mL or 12.5 μg/mL of total active ingredients.

A total of 10 Southern yellow pine sapwood samples cut from parentboards comprising on average 5 to 10 annual rings per inch were immersedin the test solutions for 3 minutes, followed by brushing to cover anyuntreated areas. The samples were allowed to dry for 15 days at ambientlaboratory conditions and five samples having the closest preservativeuptake were selected for testing according to the AWPA E24-12 standardmold exposure test (Example 2). Untreated control samples were immersedin water for 3 minutes and allowed to dry for 15 days. Samples weresuspended in the humidity chamber, four inches above a soil bedinoculated with Aureobasidium pullulans, Aspergillus niger, Penicilliumsp and Alternaria tenuissima. Samples were observed for mold growth at2, 4, 6, 8 and 10 weeks exposure, and were rated as follows:

-   -   0—No growth;    -   1—Mold covering up to 10% of surfaces;    -   2—Mold covering between 10 to 30% of surfaces;    -   3—Mold covering between 30 to 70% of surfaces;    -   4—Mold covering greater than 70% of surfaces;    -   5—Mold covering 100% of surfaces with intense color.

The results are shown in Table 9:

TABLE 9 Dilution Average (Conc. of retention of Mold growth rating totalactive active (average of 5 replicates) ingredients) ingredients 2 4 6 810 Formulation (μg/mL) (μg/cm²) weeks weeks weeks weeks weeks UntreatedN/A 0.0 2.2 3.4 4.6 4.8 5.0 controls    (0.0) Test 373:1  0.4 0.0 2.83.0 3.4 3.4 Formulation M   (12.5) Comparative 0.4 00 2.8 3.2 3.6 3.8Formulation N Comparative 0.6 0.0 2.6 3.2 3.6 4.0 Formulation OComparative 0.5 0.0 3.2 3.4 3.6 4.0 Formulation P Test 93:1 2.5 0.0 2.23.0 3.4 3.4 Formulation M  (50) Comparative 2.1 0.0 2.4 3.4 3.6 3.8Formulation N Comparative 1.8 0.0 3.0 3.2 3.4 3.4 Formulation OComparative 1.8 0.0 2.8 3.2 3.6 3.6 Formulation P Test 47:1 4.0 0.0 1.42.4 2.4 2.6 Formulation M (100) Comparative 3.3 0.0 1.6 2.2 2.6 2.8Formulation N Comparative 3.0 0.0 2.2 2.6 2.8 2.8 Formulation OComparative 2.8 0.0 2.6 2.8 3.0 3.0 Formulation P Test 19:1 7.6 0.0 1.41.8 2.2 2.2 Formulation M (250) Comparative 6.9 0.0 1.2 2.0 2.4 2.4Formulation N Comparative 7.0 0.0 2.0 2.0 3.0 3.0 Formulation OComparative 5.8 0.0 2.0 2.4 3.4 3.6 Formulation P Test  9:1 17.4 0.0 1.01.4 1.6 2.0 Formulation M (500) Comparative 15.8 0.0 1.0 1.2 1.4 2.6Formulation N Comparative 16.8 0.0 1.2 1.4 1.6 2.4 Formulation OComparative 13.5 0.0 1.4 2.8 3.4 3.6 Formulation P Test  5:1 32.5 0.00.6 1.2 1.4 1.4 Formulation M (900) Comparative 29.2 0.0 0.6 1.0 1.4 1.6Formulation N Comparative 26.9 0.0 0.4 1.8 2.0 2.2 Formulation OComparative 24.7 0.0 1.2 2.2 2.4 2.8 Formulation P

As seen in Table 9 and FIG. 10A, test formulation M showed bettercontrol of mold growth than any of the comparative formulations N, O orP after 10 weeks of exposure, especially at concentrations of 250 μg/mLto 900 μg/mL. In contrast, untreated control samples were completelyovergrown by test fungi after this exposure time, as can be seen at theright side of FIG. 10B.

The embodiments described herein are intended to be illustrative of thepresent compositions and methods and are not intended to limit the scopeof the present invention. Various modifications and changes consistentwith the description as a whole and which are readily apparent to theperson of skill in the art are intended to be included. The appendedclaims should not be limited by the specific embodiments set forth inthe examples, but should be given the broadest interpretation consistentwith the description as a whole.

1. An antimicrobial wood preservative comprising an antimicrobial composition, wherein the antimicrobial composition comprises: about 10% to about 25% by weight of 3-iodo-2-propynyl N-butyl carbamate (IPBC); about 12% to about 20% by weight of propiconazole; about 2% to about 8% by weight of carbendazim; about 2% to about 4% by weight of a co-emulsifier, wherein the co-emulsifier comprises a first non-ionic surfactant and a second non-ionic surfactant, wherein the first non-ionic surfactant has a lower hydrophilic-lipophilic balance (HLB) than the second non-ionic surfactant; and about 25% to about 70% by weight of a carrier fluid; wherein the antimicrobial composition is in the form of a suspoemulsion wherein the IPBC and the carbendazim are present in solid form and are dispersed in the antimicrobial composition as finite particles and wherein the propiconazole is provided as a solution in a glycol solvent.
 2. The antimicrobial wood preservative according to claim 1, wherein the antimicrobial composition further comprises about 7% to 15% by weight of an emulsifier.
 3. The antimicrobial wood preservative according to claim 2, wherein the emulsifier comprises an anionic surfactant.
 4. The antimicrobial wood preservative according to claim 2, wherein the emulsifier comprises a non-ionic surfactant.
 5. The antimicrobial wood preservative according to claim 1, wherein the ratio by weight of the first non-ionic surfactant to the second non-ionic surfactant is from about 90:10 to about 80:20, and the co-emulsifier has a combined HLB of from about 4 to about
 10. 6. The antimicrobial wood preservative according to claim 1, wherein the antimicrobial composition further comprises about 3% to about 14% by weight of an emulsion stabilizer.
 7. The antimicrobial wood preservative according to claim 6, wherein the emulsion stabilizer is kaolin.
 8. The antimicrobial wood preservative according to claim 1, wherein the carrier fluid is selected from water, glycols, and mixtures thereof.
 9. The antimicrobial wood preservative according to claim 1, wherein the antimicrobial composition further comprises from about 0.3% to about 3% by weight of a defoaming agent.
 10. The antimicrobial wood preservative according to claim 1 wherein the finite particles have a particle size from about 0.1 μm to about 10 μm or from about 10 μm to about 35 μm.
 11. The antimicrobial wood preservative according to claim 1, wherein the antimicrobial composition comprises: about 10% to about 25% by weight of 3-iodo-2-propynyl N-butyl carbamate (IPBC); about 12% to about 20% by weight of propiconazole; about 2% to about 8% by weight of carbendazim; about 7% to 15% by weight of an emulsifier; about 3% to about 14% by weight of an emulsion stabilizer; about 0.3% to about 3% by weight of a defoaming agent; about 2% to about 4% by weight of a co-emulsifier, wherein the co-emulsifier comprises a first non-ionic surfactant and a second non-ionic surfactant, and wherein the first non-ionic surfactant has a lower hydrophilic-lipophilic balance (HLB) than the second non-ionic surfactant, wherein the ratio by weight of the first non-ionic surfactant to the second non-ionic surfactant is from about 90:10 to about 80:20 and the co-emulsifier has a combined HLB of from about 4 to about 10; and about 25% to about 70% by weight of a carrier fluid; wherein the antimicrobial composition is in the form of a suspoemulsion wherein the IPBC and the carbendazim are present in solid form and are dispersed in the antimicrobial composition as finite particles, wherein the finite particles have a particle size from about 0.1 μm to about 10 μm or from about 10 μm to about 35 μm, and wherein the propiconazole is provided as a solution in a glycol solvent.
 12. The antimicrobial wood preservative according to claim 1, prepared by incorporating the antimicrobial composition as defined in claim 1 into a pre-formed wood preservative formulation.
 13. The antimicrobial wood preservative according to claim 11, prepared by incorporating the antimicrobial composition as defined in claim 11 into a pre-formed wood preservative formulation.
 14. An antimicrobial wood preservative concentrate comprising an antimicrobial composition as defined in claim 1 formulated with one or more additives, wherein the antimicrobial wood preservative concentrate comprises about 3% to about 5% by weight in total of IPBC, propiconazole and carbendazim.
 15. The antimicrobial wood preservative concentrate according to claim 14, prepared by incorporating the antimicrobial composition as defined in claim 1 into a pre-formed wood preservative formulation.
 16. An antimicrobial wood preservative concentrate comprising an antimicrobial composition as defined in claim 11 formulated with one or more additives, wherein the antimicrobial wood preservative concentrate comprises about 3% to about 5% by weight in total of IPBC, propiconazole and carbendazim.
 17. The antimicrobial wood preservative concentrate according to claim 16, prepared by incorporating the antimicrobial composition as defined in claim 11 into a pre-formed wood preservative formulation.
 18. An antimicrobial wood preservative comprising the antimicrobial wood preservative concentrate of claim 14 and water, wherein the ratio of antimicrobial wood preservative concentrate to water is from 1:4 to 1:25 by volume.
 19. An antimicrobial wood preservative comprising the antimicrobial wood preservative concentrate of claim 16 and water, wherein the ratio of antimicrobial wood preservative concentrate to water is from 1:4 to 1:25 by volume. 